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We used immunohistochemical techniques to demonstrate the distribution of receptors for the cytokine tumour necrosis factor-α on the popliteal lymph node and the adipose tissue surrounding it for 5 d following a simulated immune challenge to one hind leg in the rat. We found different patterns of expression of receptors on adipocytes surrounding a lymph node to a distance of about 1 mm, and on those more remote from the node. Sites recognised by an antibody to type I tumour necrosis factor receptors appeared on the challenged node and the adipocytes surrounding it within 30 min of an injection of bacterial lipopolysaccharide, but appeared on adipocytes surrounding the unchallenged popliteal node only 24 h later. Adipocytes distant from the node, both within the same depot and in the contralateral depot, showed no response. Sites recognised by an antibody to type II tumour necrosis factor receptors were present at all times on lymph nodes and the adipocytes close to them, but appeared on more distant adipocytes only 24 h after immune challenge, in both challenged and unchallenged legs. These data support the proposal, based on in vitro studies, that the adipose tissue surrounding major lymph nodes is specialised to respond to cytokines derived from lymphoid cells, and participates in the immune responses of the adjacent node.

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This study seeks to establish the normal serum concentrations of biochemical markers related to nutrition, inflammation and disease, and to investigate how the levels change with age and diet in the rat. To this end, we fed rats from weaning on three diets differing in their protein, carbohydrate and fatty acid content. The diets consisted of a control, nutritionally balanced diet, this same diet supplemented with 10% (wt/wt) beef tallow, and a diet that was high in fat and carbohydrate and low in protein. Blood samples from rats at two different ages, 3 months and 12 months, were then analysed. In control rats, with advancing age there was a general decrease in potassium, iron and serum albumin concentrations and in the activities of aspartate aminotransferase and alanine aminotransferase, and an increase in total and HDL cholesterol. These changes were modulated by diet: many of the age-related changes (serum concentrations of potassium, iron and cholesterol, and liver enzyme activities) were not observed in animals eating the high fat diet. In contrast, the high carbohydrate, high fat, low protein diet-fed animals showed several additional changes (serum concentrations of sodium, urea, creatinine and TG, and activity of alkaline phosphatase) that can be related to kidney, liver and cardiovascular health